a. Field of the Invention
This invention relates to suspension liners adapted to provide an interface between a residual limb and a prosthetic socket.
b. Discussion of Related Art
The use of suspension liners adapted to provide a soft, flexible interface between a residual limb of an amputee and a hard socket to which a prosthetic device is secured is known in the art generally, as exemplified by U.S. Pat. No. 4,923,474. Such suspension liners are typically made of an air impermeable elastomer material such as silicone and may include a reinforcement layer intermediate the inner and outer surfaces of the suspension liner body portion or externally thereof to provide resistance against axial elongation of the elastomer constituting the suspension liner body. Such reinforcement typically does not restrict radial distension or stretching of the suspension liner body.
In accordance with prior art teachings, these suspension liners may function to secure the residual limb within the prosthetic socket member once the residual limb and sleeve are inserted into the socket in a close-fitting relationship by isolating the distal end area of the hard socket from the atmosphere. Upon application of a pulling force on the suspension liner relative to the socket, suction is created in the distal end of the socket tending to retain the suspension liner within the socket. Appropriate devices are usually provided to enable expulsion of air between the distal end of the suspension liner and the hard socket, and to isolate the distal end of the hard socket member from the atmosphere after the suspension liner with a residual limb has been fully inserted within the socket member.
In some applications, the suspension liner is provided with an umbrella at its distal end and a threaded socket for receiving a prosthetic securing pin member which then extends through an axial opening in the distal end of the hard socket member for securing the socket member relative to a prosthetic device mounted to the distal end of the socket member.
In other applications, the prosthetic device is secured to the exterior of the distal end of the hard socket member and the sleeve member is fully contained within the hard socket member.
The elastomer constituting the suspension liner member frictionally engages and remains attached to the skin of a residual limb so that the limb is retained within the hard socket member in a comfortable, non-irritating manner. The suspension liner may be thickened to provide cushioning effect between the residual limb and the hard socket, which is typically custom made to closely fit the residual limb. Suspension liners of this kind are used for both trans-tibial (TT) amputees as well as trans-femoral (TF) amputees. That is, the suspension liners may be utilized for applications above the knee or below the knee of the amputee.
In other applications, it may be desired to more positively secure the suspension liner within the socket by creating a hypobaric (vacuum) pressure within the distal end of the hard socket between such distal end and the distal end of a suspension liner inserted into the socket with a residual limb contained within the suspension liner. The hypobaric pressure may be maintained at the distal end of the hard socket and the interior of the socket at its distal end will be isolated from atmosphere during normal retention of the sleeve liner within the socket. Opening the distal end of the socket to atmosphere releases the vacuum or hypobaric pressure within the socket to enable simple withdrawal of a residual limb with a suspension liner thereon from the socket.
A pump or other device may be utilized to evacuate the distal end of the socket between the distal end of a suspension liner and the distal end of a socket. A valve or other appropriate device typically is used to open and close the distal end of a socket to surrounding atmosphere.
Various arrangements are known in the prior art for providing an appropriate seal between the exterior of the suspension liner and the interior of the hard socket including external air impermeable sleeves covering the interface area between the proximal end of the hard socket and the adjacent suspension liner body.
In trans-femoral applications, the sealing between a suspension liner and a socket is generally simpler and easier to execute than sealing a trans-tibial suspension liner against the inner surface of a socket because in the latter situation, the residual limb contains more bony protuberances and irregular shapes that are difficult to effectively seal, particularly if it is desired to simply use the material of the elastomeric suspension liner as the sealing element.
While many of these known suspension sleeves having seal have been effective, it has been found that there are variations in the hard sockets including open spaces that minimize the effectiveness of the seal elements. Moreover, the residual limbs have a tendency to undergo volume fluctuations that may impair the success of the sealing interface between the seal element and the hard socket.